The present invention relates to a machine for glueing and folding sheet-like materials. In particular, the invention relates to an automatic machine for folding the edges of workpieces of leather, plastics, fabric and the like, and especially the peripheral edges of shoe uppers.
Various kinds of machines for folding and glueing the edges of shoe uppers, both manually controlled and with partly automatic control, are known.
From a general point of view, a current folding machine comprises a worktable, on which the workpiece to be peripherally hemmed is caused to slide, and an advancement shaft connected to a motor; the speed of said motor is normally adjustable by means of a clutch actuatable by the operator. The advancement shaft actuates various elements for reciprocatingly moving the workpiece according to advancement lengths (the so-called advancement pitch) which are mechanically preset by moving terminal stop elements; the advancement lengths may be changed during treatment by means of an electromagnet or of another kind of actuator in an alternating manner starting from one stop element up to the opposite one. The elements for folding a portion of the peripheral edge of the workpiece comprise a folding foot which co-operates with a fixed abutment and an oscillating finger for folding the edge of the workpiece against the folding foot. Presser means are furthermore provided to retain and advance the folded workpiece. The folding foot is normally axially hollow and the glue is fed through it onto the edge portion to be folded; said glue is fed by means of a geared pump which is actuated mechanically in some cases and by means of direct-current motor or step-motor servomechanisms in other cases; the glue is dispensed at the lower end of the foot in a preset manner proportionally to the rotation rate of the machine and to the length of the advancement pitch. The machine furthermore comprises a cutting blade which is actuated when the edge to be folded has an inward or concave curvature and cuts the border of the workpiece to facilitate the folding of the inward curves.
The most recent machines furthermore have a system of photocells or light-responsive elements arranged in the worktable so as to recognize the presence and the shape of the workpiece and consequently automatically control, by means of appropriate processor circuits, the beginning and the end of the dispensing of the glue and the reduction of the pitch in the outward curves to be folded; the pre-adjustment of the glue dosage is instead controlled by the operator. The same photocells can cause the actuation of the cutter blade, which can be actuated in combination with the pitch reduction; the pitch is in any case always preset mechanically by the operator.
In folding machines of the above described type the rotation rate of the machine is normally adjusted by the operator, who acts on a clutch, generally included in the main motor, by means of a pedal. Therefore particular care and responsibility by the operator is required, since he must adapt the speed of the machine to the various shapes and dimensions of the workpieces.
If the type of workpiece or the shape and quality of the material of the workpiece are changed, the machine must be adjusted to adapt it to the characteristics of the new workpieces.
This in practice entails an onerous work, besides significant wastes of time and therefore of productivity, since said adjustments must be performed rather frequently during the workday.
The manual adjustment of the various operative parameters of the machine furthermore entails the possibility of errors which cause the production of incorrectly treated workpieces.